Embodiments of the present invention relate to a projection display and a method for projecting an overall image. Further embodiments of the present invention relate to a projection display for virtual images with multichannel optics.
Head-mounted displays (HMD) are commonly realized with a micro display, such as an LCD (liquid crystal display), LCoS (liquid crystal on silicon) or OLED (organic light emitting diode)-based micro display, in connection with ocular optics which maps the micro display to a distance suitable for visualization between the distinct visual distance and infinity. The focal length of the ocular fOk determines, together with the diagonal D of the micro display, the field of view (FOV) of the head-mounted display:
                    FOV        =                  2          ⁢                                          ⁢          atan          ⁢                      D                          2              ⁢                                                          ⁢                              f                Ok                                                                        (        1        )            
In order to obtain common fields of view of head-mounted displays in the range between 40° and 60° with available micro imagers with typical diagonal screens of ⅔″, ocular focal lengths in the range between 15 and 23 mm are necessitated. Here, the pupil diameter of the ocular Dpupil determines the size of the range within which the eye of the viewer can move (eye motion box, EMB). The pupil size or EMB is obtained from the ratio of focal width fOk and f-number f/# of the ocular:
                    EMB        =                              D            Pupille                    =                                    f              Ok                                      f              #                                                          (        2        )            
For typical f-numbers in the range of approx. f/2.8, an EMB of the order of magnitude of 5 to 8 mm is obtained. Here, two main problems appear. On the one hand, the comparatively large necessitated ocular focal length results in large system dimensions, which deteriorates the wearing comfort of the head-mounted display. On the other hand, the low f-number necessitated for a large EMB together with the large FOV makes the correction of mapping errors more difficult, which increases the complexity (and hence the size and mass) of the ocular optics even further.
In order to reduce the size of the optics with the given focal length, in conventional technology, for example, optical paths folded several times, such as in the “Canon Video see-through” system as in (A. Takagi, S. Yamazaki, Y. Saito, and N. Taniguchi “Development of a stereo video see-through HMD for AT systems”, in Int. Symp. On Augmented Reality, Munich, Germany, Oct. 5-6, 2000), or a displacement of the ocular optics in the direction of the side pieces with subsequent image guide for mirroring into the eye, such as in (Ichiro Kasai Yasushi, Yasushi Tanijiri, Takeshi Endo, Hiroaki Ueda “A Forgettable Near Eye Display”, Proc. 4th Int. Symp. on Wearable Computers, ISWC 2000, Atlanta), are used. The main disadvantages of these known optics schemes are the resulting comparatively large system dimensions and masses as well as the complicated free form optics necessitated for aberration correction according to conventional technology, such as in (A. Takagi, S. Yamazaki, Y. Saito, and N. Taniguchi, “Development of a stereo video see-through HMD for AT systems”, in Int. Symp. On Augmented Reality, Munich, Germany, Oct. 5-6, 2000), or image guide elements that are very complex to produce, such as in (Ichiro Kasai Yasushi, Yasushi Tanijiri, Takeshi Endo, Hiroaki Ueda “A Forgettable Near Eye Display”, Proc. 4th Int. Symp. on Wearable Computers, ISWC 2000, Atlanta).
An alternative optical approach described in conventional technology uses lens array (lens grid) optics, wherein one lenslet (lens element) is allocated to one pixel of a micro imager each, as is described in U.S. Pat. No. 5,499,138, U.S. Pat. No. 5,561,538, U.S. Pat. No. 6,816,313 B2 and US 2008/020473 A1. While this known alternative optics scheme promises a very small structural length of the optics, it allows only a very small displayable number of pixels and a very low transmission, resulting in a low image brightness and short battery run-time for network-independent devices.
A further known approach is the usage of an array projector or raster projector, as is described in WO 2010/145784 A1). With this approach, clearly greater image brightness can be obtained as compared to the array optics or raster optics described in U.S. Pat. No. 5,499,138, U.S. Pat. No. 5,561,538, U.S. Pat. No. 6,816,313 B2 and US 2008/020473 A1. However, the known array projector based on multichannel projection has, the disadvantage that the displayable number of pixels still lags behind the single-channel optics, such as in (A. Takagi, S. Yamazaki, Y. Saito, and N. Taniguchi, “Development of a stereo video see-through HMD for AT systems”, in Int. Symp. On Augmented Reality, Munich, Germany, Oct. 5-6, 2000) and (Ichiro Kasai Yasushi, Yasushi Tanijiri, Takeshi Endo, Hiroaki Ueda “A Forgettable Near Eye Display”, Proc. 4th Int. Symp. on Wearable Computers, ISWC 2000, Atlanta).
U.S. Pat. No. 6,611,241 B1 describes large optical displays comprising an array of smaller display devices or modules, each of which showing part of the image to be displayed, so that the array of smaller display devices together displays the complete image. The display device can use display elements having no narrow edges and that are not contiguous in order to generate overlapping sub-images. Image pixels that are otherwise “interfaces” or gaps are generated by the image data and displayed at the correct position and brightness within the displayed image, such as in the overlap regions of the overlapping sub-images.
WO 2011/157632 A1 describes a projection display having at least one light source, at least one reflective imager that is implemented to display individual images in a two-dimensional distribution of sub-areas, a projection optics array with a two-dimensional array of projection optics, which is implemented to map an allocated sub-area of the at least one imager to one image level each, so that mappings of the individual images overlap to an overall image in the image plane, and at least one beam splitter that is arranged in an optical path between the at least one reflective imager and the two-dimensional array of projection optics on the one hand and in the optical path between the at least one light source and the at least one reflective imager on the other hand.
U.S. Pat. No. 5,499,138 describes an image display apparatus, such as an image display apparatus of the spectacle type which is able to reproduce a high-resolution image by projecting pixels at a correct pitch on the retina in the eye of the user. The image display apparatus comprises a microlens array. Instead of the microlens array, a Fresnel zone plate array can also be used.
A disadvantage of the projection system described in U.S. Pat. No. 5,499,138 is the allocation of only one (single) display pixel (e.g. very small LED chip or LCD pixel) to one microlens each. Thus, this known approach results in a lower displayable number of pixels with at the same time large lateral optics dimensions.
Hence, it is a basic problem that no concept exists in conventional technology which unites multichannel projection for a larger number of displayable pixels with a small structural length of a projection display.